1. Field of the Invention
The embodiments discussed herein are related to a manufacturing method of a silicon carbide semiconductor apparatus.
2. Description of the Related Art
Conventionally, silicon carbide (SiC) semiconductors are stable thermally, chemically, and mechanically, and application thereof as light emitting elements and high frequency devices, power semiconductor apparatuses (power device), etc. is expected in various industrial fields. In particular, high breakdown voltage metal oxide semiconductor field effect transistors (MOSFET) using a SiC semiconductor have an advantage of having an ON resistance that is lower than power devices that use a silicon (Si) semiconductor. Further, a Schottky diode that uses a SiC semiconductor has been reported to have a lower forward voltage drop than a Schottky diode that uses a silicon semiconductor.
Although the ON resistance and switching speed of a power device have a trade-off relationship, power devices using a SiC semiconductor have the potential of concurrently achieving low ON resistance and high switching speed. In lowering the ON resistance of a power device that uses a SiC semiconductor, reduction of the contact resistance of an ohmic contact (electrical contact unit) formed between an electrode film and a SiC semiconductor portion is important. Further, to increase the switching speed of the power device, the contact resistance of the ohmic contact with respect to the SiC semiconductor portion is a significant problem. Concerning this point, one problem in practical application of a power device that uses a SiC semiconductor is that a technique for forming an ohmic contact of a low resistance suitable for practical use and adaptable for production (manufacturing) processes and structures of devices has not been sufficiently established.
For example, a method of depositing an electrode film on the n-type SiC semiconductor portion and subjecting a formed ohmic electrode structure to heat treatment at a high temperature on the order of 800 to 1200 degrees C. has been proposed and is a conventional technique widely used to form a low resistance ohmic contact of the n-type SiC semiconductor portion (for example, refer to Japanese Patent Application Laid-Open Publication No. 2004-335899 (paragraphs 0038 to 0039)). Nickel (Ni), tungsten (W), and titanium (Ti) are commonly known electrode materials (for example, refer to Japanese Patent Application Laid-Open Publication No. 2004-335899 (paragraph 0053) and Japanese Patent No. 5565895 (paragraphs 0011 to 0013)). In particular, an ohmic contact using nickel as an electrode material obtains a contact resistance value on the order of 10−6 Ωcm2, which is suitable for practical use and very promising as ohmic contact.
When nickel is used as an electrode material, the nickel film and SiC semiconductor portion react consequent to the high-temperature heat treatment and a reaction layer (e.g., nickel silicide (NiSi) film) of a mixed conductivity of nickel-silicon-carbon (C) is formed as an electrode film. In this case, consequent to the generation of the reaction layer, a significant amount of carbon atoms separated (diffused) from the SiC semiconductor portion are deposited near the surface of the electrode film, and electrode film surface is substantially covered by a carbon layer formed by the deposition of the separated carbon atoms. Therefore, because of the carbon layer deposited on the electrode film surface, adhesion of the electrode film and a wiring film of aluminum (Al), etc. further stacked (formed) on the electrode film for wiring becomes poor, and may cause peeling of the wiring film. To suppress the peeling of the wiring film, after the wiring film is deposited by a relatively high temperature, the carbon layer deposited on the surface of the wiring film has to be physically and/or chemically removed.
As described, when nickel is used as an electrode material, carbon atoms separated from the SiC semiconductor portion are deposited in the surface of the electrode film (nickel silicide film) that is formed by high temperature heat treatment and a problem arises in that these deposited carbon atoms cause the wiring film such as an aluminum film, etc. formed on the electrode film to be susceptible to peeling.